Water cooled retort cover



May 8, 1962 w. J. ASH ETAL WATER COOLED RETORT COVER Filed Aug. 12, 1960INVENTORS WILLIAM J. ASH

E POZZI JOHN BY United States Patent 3,033,549 WATER COOLED RETORT COVERWilliam J. Ash, Salisbury and John F. Pozzi, North Canaan, Conn.,assignors, by mesne assignments, to the United States of America asrepresented by the United States Atomic Energy Commission Filed Aug. 12,1960, Ser. No. 49,396 2 Claims. (Cl. 266-19) This invention relates toimproved apparatus for the recovery of volatizable metals such asmagnesium in substantially pure form wherein the metal to be recoveredis first vaporized and then condensed. In particular, the inventionpertains to a new and improved retort cover which provides a condensingsurface for the vaporized metal and means for maintaining the saidsurface within a desired temperature range.

In the production of magnesium the raw material from which the metal isto be produced is placed in the hot end of a tubular steel retort andsubjected to a high temperature of about 2l50-2200 F. and a vacuum ofabout 100 microns. This end of the retort is located within a furnace inorder to maintain the necessary high temperature. The other or cold endof the retort is located outside the furnace and has a removable head orclosure which is furnished with a gasket to make the retort vacuumtight. This gasket must be protected from excessive heat which woulddamage it and destroy the seal thereby permitting inleakage of air andloss of vacuum. On the other hand, it is known that if magnesium iscondensed at too low a temperature the deposit is finely divided andpyrophoric. Therefore the temperature of the condensing surface for themetal must be maintained sufiiciently high to cause the magnesium to bedeposited 'in massive form, in which condition it may be safely handledin air even 'at elevated temperatures. It is accordingly an object ofthis invention to provide a new and improved retort cover which is soconstructed and arranged as to provide a high temperature condensingsurface for the magnesium vapors while simultaneously protecting theretort gasket from damage due to excessive temperatures.

Another object is to provide a retort cover having its sealing surfaceisolated fromthe region of hot metal by closely disposed water cooledsurfaces which act as cold traps in preventing th passage of hot watervapors.

The invention may be better understood by reference to the accompanyingdrawings wherein:

FIG. 1 is a cross section showing the general arrangement of a retortassembly when employing the invention; and

FIG. 2 is a cross sectional view taken along line Il -II of FIG. 1.

As shown in FIG. 1, the assembly consists of a tubular, stainless steelretort mounted in a furnace wall 11 of a refractory material, such asbrick, and closed by a cast stainless steel cap 12 at its inner end. Thematerial to be heated is indicated schematically at 13. In the practiceof this invention it is important that this starting material besubstantially free of metal compounds having higher vapor pressures thanthose of the magnesium being produced. Specifically, impurities in theraw material that generate sodium or potassium must be avoided, if thefinal condensed metal deposit is to be of high quality magnesium.

At its outer end the retort is provided with a slightly enlarged section14 which is joined to section 10 by an intermediate section 15. At thepoint where the retort assembly emerges from the refractory furnace wall11, a stainless steel wrap 16 encases section 15.

An annular flange 17 is welded to the outer end of secthen remainssubstantially uniform Patented May 8, 1962 tion 14, which outer end issurrounded by a water jacket 18 having connections 19 and 20.

A perforated plate 21 separates the hot and cold ends of the retort andserves to reduce heat losses.

In order to evacuate th retort, a conduit 22 communicates with theinterior of the retort and may be attached to a suitable vacuum pumpingmeans (not shown).

A condensing sleeve 23 is located within the section 14 of the cool endof the retort to receive the condensed deposit'of metal indicatedschematically by 24. The elements heretofore described are old in theart and form no part of the present invention.

The novel and improved portion of the assembly illustrated in FIG. 1consists of the retort cover. This comprises a circular steel coverplate 25 provided with a pair of handles 26, one of which is shown inthe drawing, FIG. 1. A pair of brackets 27 engage the flange 17 andposition the cover over the open end of the retort. An annular shoulder28 on the cover plate positions a neoprene gasket 29 which engages aboss 30 on the flange 17 to seal the cover to the retort.

A stainless steel cylindrical section 31 slightly smaller in diameterthan the condensing sleeve 23, is welded at one end to the cover plateat 32. The opposite end of section 31 is closed by a mild steel disc 33which is welded thereto as indicated at 34. The Zone or chamber soformed is divided by a mild steel partition 35 into two approximatelyequal compartments 36 and 37. At the extreme upper portion of thepartition 35 a hole or opening 38 is provided to permit introduction ofa granular mineral insulating material into the compartment 36 to thelevel indicated by 39. The opening permits escape of any steam generatedin the insulating material during operation of the retort.

A water connection 40 permits water to be introduced or withdrawn fromcompartment 37. The water level 41 in this compartment is determined bythe position of a further opening 42 in the cover plate 25 at a distancebelow the opening 38 in partition 35.

In operation, the retort is loaded with a magnesium containing materialin the form of briquettes as schematically indicated at 13, thebriquettes being substantially free of metal compounds such as sodiumand potassium having higher vapor pressures than magnesium. Theperforated plate 21 is placed in position. After the condenser sleeve isinserted and the head is put on, the retort is evacuated through conduit22. This is accomplished in two steps, first a roughing vacuum down toabout 1500 microns pressure, followed by a fine vacuum down to operatingpressure of about microns. The application of the vacuum holds the coversealed against the flange 17.

Heat is applied to the end of the retort containing the charge, andwater is introduced into the compartment 37 either through theconnection 40 or through the opening 42. As heat continues to be appliedto the retort, the temperature of the steel disc 33 rises rapidly, dueto both outgassing and radiation to approximately 500 F., at whichtemperature a state of equilibrium is reached with no substantial changetaking place in the temperature of the disc until evolution of magnesiumvapor commences. At this time another sharp increase in the temperatureof the disc takes place. In the case of magnesium, the temperature ofthe plate may reach 900 F. to approximately the melting point ofmagnesium, 1204 F. The temperature for a period of ap proximately twohours, after which the temperature of the disc slowly declinesthroughout the balance of the cycle, eventually reaching 600 F. to 800F. This slow decrease in temperature is probably a result of theincreasing thickness of the metal deposit, causing the actualcondensation zone to move progressively away from the disc so that anincreasing amount of heat is transmitted to the Water jacket 18;Simultaneously with the deposit of magnesium on the disc 33, depositionoccurs on the inner surface of the sleeve 23.

Throughout the condensation cycle, water is maintained in thecompartment 37 to cool the cover plate 25'. The Water in thiscompartment, in combination with the Water in the jacket 18, protect thegasket 29 from overheating. Use of the construction of this inventionhas fully and clearly established the fact that in both experimental andcommercial production operations the life of the gasket has beenmaterially extended.

Upon completion of the condensation cycle, the vacuum connection isclosed and air is introduced into the retort. After the vacuum in therotor has ben broken, the cover is given a sharp blow with a heavy bar,thereby separating the cover from the magnesium deposit. The cover isthen lifted from the retort, the sleeve is next removed and themagnesium deposit is recovered therefrom.

In practice it has been found that the surface of the disc 33 shouldpreferably be covered with an oxide coating before its initial use. Thiscoating may be applied by washing the cover with a lime solution. Aftersuch treatment, the disc 33 will break clean of the deposited magnesiumupon completion of the cycle. The same clean break will occur withcovers that have once been used, as the conditions prevailing in theprocess will cause an iron oxide coating to form on the condensingsurface 33. Covers not having an oxide coating on the condensing surfacemay adhere to the deposited magnesium and are therefore to be avoided.

It will be readily seen that the axial location of the plate 35 may bemodified to effect changes in the ultimate temperature reached by theplate 33. For example, a decrease in the thickness of the volume 36accompanied by an increase in the thicknes of the volume 37, therebyincreasing the ratio of the water cooled zone to the insulated zonewould permit a lower temperature to be reached in 33. Conversely, movingthe plate 35 tothe right in FIG. 1 will increase the ratio of insulationto water and result in an increased maximum operating temperature on theplate 33. These variations in the configuration are necessary to adjustthe temperature of the plate 33 to a satisfactory level for the rate ofevolution of the metal being condensed. For example, in the productionof magnesium in a retort of approximately in inside diameter and 10'6"overall length, it has been found that the outside diameter of thecylinder 31 should be approximately 9%", that the axial length of thespace 36 should be approximately 2 that the axial length of the space 37should be approximately 2%". In this example, the plate 33 is A" thick,the plate 35, thick and the plate 25, /2' thick.

In the practice of this invention, any suitable insulating material,even air, may be used in compartment 36, the kind and amount of suchinsulation being regulated as needed to provide a condensing surface at33 at the highest possible temperature for the prevailing pressure inthe retort. By reason of the high temperature of condensation, themagnesium deposit on the end Wall of the cover is extremely dense. Incontrast, experiments in which the condensing surface was directly Watercooled proved a failure as the magnesium condensed too rapidly andproduced a finely divided pyrophoric rather than a dense deposit.

We claim:

1. A retort cover comprising a cover plate, sealing, means on said platefor scaling the cover to a retort, a tubular corrosion. resistant metalsection secured at one end to the cover plate, a condensing surfacesecured to the other end of the tubular section to define With saidcover plate a zone, a partition in said Zone parallel to the cover plateand subdividing the zon into two compartments, one adjacent thecondensing surface and one adjacent the cover plate respectively,insulating means in the compartment adjacent the condensing surface andmeans for introducing a coolant into the compartment adjacent the coverplate.

2. A retort cover comprising a cover plate, sealing means on said platefor sealing the cover to a retort, a tubular corrosion resistant metalsection secured at one end to the cover plate, a condensing surfacesecured to and closing the other end of the tubular section and definingwith the cover plate a zone, a partition in said zone. parallel to thecondensing surface and to the cover plate and subdividing the zone intotwo approximately equal compartments, one adjacent the condensingsurface and one adjacent the cover plate, means at the top of saidpartition defining an opening, means in the cover plate defining anopening below the opening in the partition, insulating means in thecompartment adjacent the condensing surface, and means for introducing acoolant into the compartment adjacent the cover plate.

OTHER REFERENCES American Institute of Mining and MetallurgicalEngineers, vol. 159, 1944 (pages 317-322, 368 and 369).

